I know you have had a lot of patience, and that patience is herebye rewarded. Just in time as this is the winemakers season !!!!This is the fifth and last part about measuring acidity in a juice, must or wine.

The first part (click here to re-read) showed you how to measure acidity with a titration kit. This method is perfectly suitable for clear juices. However the measurement is based on a color change which is harder to notice in a dark juice. Therefore this method is less suitable for dark juices.

The next parts in this series where a quest for the search for an ideal method to measure acidity in a dark juice. I will give here a quick tour.

Part 2 (click here to read) showed that a dark juice could be dilluted to better notice the color change.

Part 3 (click here to read part 3) investigated a method that is described in a magazine and sometimes mentioned on a forum. The method discolors a juice by using active coal. Part 3 definitively showed why this is not a good idea.

Part 4 (click here) demonstrated a method used often by members of forums. It is often called the reverse method. This method works great for measuring acidity in a dark juice, must or wine.

So if part 2 and 4 describe a good method for measuring acidity in a dark juice why even bother with a fifth part.

Well, in this part I am going to demonstrate the easiest method for measuring acidity in a dark juice. This method works equally well for a clear juice. I have used this method for many years myself with great ease and success. Off course I do not want to keep it from you.

Sometimes this method is called (in error) paper chromotography. This is indeed an error as this is not really paper chromotography. A better name is the 'white tile' method. This all sounds complicated however it is not. it is simplicity itself.

To simplyfy things I have made a sample form for you. You can download it by clicking it. Print this form several times and keep it somewhere safe. This makes sure that you have a form available when you need it most.

The theory

The theory is simple, just like using the method in real life.

The hard part in titrating acidity in a dark juice is to determine when color changes. Now by putting a small drop of the titrated juice on a white background, the color change will be easily noticable.

Real life examples.

In real life this is indeed the most easiest method of measuring acidity. Let's get started right away. I'll show you a few samples.

For this story I used the same wines as I used in part 4. I just did not use the reverse method, but a straight titration. Follow the story here and all will be obvious.

I started with a red wine.

First the measuring tube was filled with the wine till the 0-marker.

Next I took a small drop out of the testing tube and dropped it on the sheet of paper in the square marked 0. As you can see, it made a nice red dot.

The second step was to add blue-indicator (just like with a normal titration) till the 1-marker was reached. The fluids were mixed carefully. Do not shake the testing tube (if you want to know why, read part one)

Again a small drop of the fluid was taken out of the testing tube and dropped on the sheet of paper at the square marked with the figure 1. And again a red drop formed on the paper.

I repeated this procedure a few times adding a bit blue-indicator each time till the next mark was reached.

When the level in the testing tube had risen to 6 a colour change was starting to show.

At the next step when the level had risen to the 7 mark the small dot on the paper was definitely a dark one. The color was almost blue. So the color had changed at 7.

For the record I made an extra step in titration. However at the 8 marker the color did not change anymore.

So the color change happened at an acidity of 7 and could very easily be detected. Off course this measurement gave exactly the same result with a normal titration and with the reverse method.

However one test does not prove anything, so on to the next.

Test 2: Apple-blackberry wine

As you may recall from part 4, the reverse method, I had an apple-blackberry wine with a high acidity. Normal titration and the reverse method showed that this wine had an acidity no less as 9. Let us see what the 'white-tile' method tells us.

As usual I started with filling the test tube with wine to the 0-marker.

I took a drop out off the test tube and dropped it on a new test-sheet at the 0 square. A nice red dot formed.

The next step was to add blue indicator to the test tube until I reached the 1-marker. Again the fluids were mixed carefully.

When mixed a drop was taken out and dropped on the test-sheet in the sqaure marked with a 1. That drop formed again a nice red dot.

Step by step the process was repeated each time adding a bit blue-indicator till the next mark was reached.

When the level in the test-tube had reached the 8-mark the color started to get darker.

At the 9-mark the color change had really happened.

So this indicated that the acidity of my apple-blackberry wine was at 9. Just like the normal titration test and the reverse method had showed. However it was more clearly visible now.

So this method works just as fine as the 'reverse-method' however it is much more easier !!!

The ultimate test: A predefined amount of acid.

The best way to test accuracy of this method is to use a fluid with a known amount of acid.

So I started with weighing 7 gram tartaric acid on a perecision scale.

Next I put this acid in a measuring beaker and filled it exactly to the 1 liter mark. This way I knew I had a fluid with an exact acidity of 7 !!

You need to use tartaric acid for this test. Why you can not use citric or malic acid is discussed in the previous story.

So I started again a normal titration by filling the test tube to the 0 marker with the acid fluid.

Like in the previous tests in this story a drop was taken out of the test tube and placed on a fresh sheet of testing paper at the square marked with a 0. The dot was off course totally clear.

I added blue-indicator till the volume reached the 1-mark and mixed the fluids carefully.

I took a drop out of the testing tube and dropped it on the test sheet at the square marked 1. The dot was clear like the previous one.

So I kep adding blue-indicator step by step and each time examining a drop of the mixture on the test sheet.

When the level reached 6 some color change became visisble.

At 7 the color change was dramatical !!!

So again this method pointed exact to the right amaount of acid.

Now I had done 3 test in which each test exactly pointed to the right amount of acid. So I can safely assure you that this method is accurate.

A note on the side:

I can hear the sceptical thinking.

Each time you take a drop out of the testing tube teh amount of acid in the tube will drop. That is off course true, and that is why you just need to pick a tiny sample.

By dipping the rear end of a spoon in the testing tube you will attach a very small drop to this end and that is just sufficient. You can also use a straw that just has to be dipped in.

Concluding:

This last part in the series showed you the easiest way of measuring acidity by titration. This white tile method is suitable for any kind of juice, must or wine.

To make things even easier you can use the test-form I prepared especially for this. you can download it as a pdf file here. print it out a few times for yuor own convenience.

If you have followed this serie, measuring acidity of any juice can not go wrong.